[PATCH] docs: add note about experimental API in LTS

[Kevin Traynor <ktraynor@redhat.com>]

The justification and impact for changing experimental API on LTS
branches is different from the main branch. So the policy that is
being used for allowing experimental APIs to change is stricter on
the LTS branches.

This was not documented anywhere, so add some documentation.

Suggested-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
---
 doc/guides/contributing/stable.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/guides/contributing/stable.rst b/doc/guides/contributing/stable.rst
index 9ee7b4b7cc..8156b72b20 100644
--- a/doc/guides/contributing/stable.rst
+++ b/doc/guides/contributing/stable.rst
@@ -127,4 +127,12 @@ but may be considered in some cases where:
 * An existing feature in LTS is not usable as intended without it.
 
+APIs marked as ``experimental`` are not considered part of the ABI version
+and can be changed without prior notice. This is necessary for the API to be
+improved and stabilized and become part of the ABI version in the future.
+
+However, in LTS releases ``experimental`` API should not be changed as there
+will not be a future ABI version on the branch and compatibility with previous
+release of an LTS version is of the highest importance.
+
 The Stable Mailing List
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-- 
2.41.0